GRACE Equivalent Water Mass Balance of the Himalayas and Tibet Plateau
Reginald R. Muskett, Geophysical Institute & the International Arctic Research Center, University of Alaska Fairbanks, AK, USA
Water Equivalent Thickness Change (cm)
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Water Equivalent Thickness Change (cm)
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y = 0.0030x + 0.2978
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Bay of Bengal Region
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Water Equivalent Thickness Change (cm)
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-20
A simple analytical sinusoidal model was
least-squares fitted to the GRACE HimalayaTibet water equivalent thickness time series.
2
The correlation of the fit was at an R of
0.82.
Himalaya and Tibet Region (red)
Model (black)
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10
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y = 0.0791x - 2.4508
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1
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+1.0 ± 0.8 km3/yr
Region 12
Least-Squares Fitted Sinusoidal
Model
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Water Equivalent Volume Change (km )
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2
-60
y = -0.1292x + 4.5576
Chambers, D.P. (2006a). Evaluation of new GRACE time-variable gravity data over the ocean. Geophys. Res., Lett., 33 (17), Li7603, doi: 10.1029/GL027296.
Chambers, D.P. (2006b). Observing seasonal steric sea level variations with GRACE and satellite altimetry. J. Geophys. Res., 111, C03010,
doi: 10.1029/2005/JC002914.
Paulson, A., S. Zhong, and J. Wahr (2007). Inference of mantle viscosity from GRACE and relative sea level data, Geophys. J. Int. , 171: 497-508,
doi: 10.1111/j.1365.246X.2007.03556.x.
Ramillien, G., S. Bouhours, A. Lombard, A. Cazenave, F. Flechtner, and R. Schmidt (2008). Land water storage contribution to sea level from GRACE geoid
data over 2003 -- 2006. Global and Plan. Change, 60, 381-392, doi: 10.1016/j.gloplach.2007.04.002.
The plot at left shows the result of removal of
the model seasonal periodic variation series
from the GRACE Himalaya-Tibet water
equivalent thickness time series. The residual
trend may be from combined sources of water
mass variation (snow accumulation / precipitation,
groundwater storage, soil water storage and
glacier ice).
Himalaya andand
Tibet Plateau
(after model
reduction)
Himalaya
TibetRegion
Region
minus
Model
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2
0
-2
-4
-6
y = -0.0311x + 0.6366
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The plots above illustrate GRACE secular trends and variations in 5 by 5 degree regions from August 2002 through December 2006. Seasonal near-periodic variations are well resolved in regions of the central Himalaya
Mountains (regions 3, 5, and 8). Resolution of the near-periodic variations decrease in region from south to north on the Tibet Plateau. Least-squares derived secular trends show water equivalent volume losses along
the arc of the main Himalaya Mountains, with water equivalent volume increases on the Pamirs and Karakoram (regions 1 and 2) and on the Tibet Plateau (regions 4, 6, 9, 10, and 12). The GRACE volume loss trends in
regions 3, 5, 8 and 11, may be following trends of negative glacier mass balance and reduction of snow cover. Are the GRACE volume gain trends in regions 4 and 5 following similar glacier mass balance trends (positive
mass balance) and expansion of snow cover? What about changes in groundwater storage? Validation with in-situ data is needed.
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Water Equivalent Thickness Change (cm)
Residual Trend (GRACE - Model)
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References:
Acknowledgements
The Japan Aerospace Exploration Agency is thanked for use of their cluster computing facilities at the International
Arctic Research Center, and the Alaska Region Supercomputing Center is thanked for providing computing facilities.
GRACE data were processed by D.P. Chambers, supported by the NASA Earth Science REASoN GRACE Project,
and are available at http://grace.jpl.nasa.gov.
GRACE regionally-averaged water equivalent
thickness time-series and least-squares trend
are show at left. The similarity of the nearperiodic Seasonal variation is significantly
positively correlated with the Himalaya-Tibet
time series. If spatial contamination is not an
issue, then the correlation suggests a strong
influence from the southern Asian monsoon
pattern. The region of GRACE data extraction
o
o
o
o
is from 0 to 22 N, and 75 E to 100 E.
Bay of Bengal Region
15
20
0
3
y = -0.0133x + 0.4863
20
-1.7 ± 2.1 km3/yr
Region 11
0
Water Equivalent Volume Change (km )
-0.2 ± 0.4 km 3/yr
Region 13
40
-20
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y = -0.0167x + 0.5399
-20
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y = -0.2533x + 8.5125
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-3.3 ± 2.8 km3/yr
Region 8
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-60
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Water Equivalent Volume Change (km )
-40
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-20
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-15
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Water Equivalent Volume Change (km )
1
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-40
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y = -0.252x + 8.5788
0
3
Water Equivalent Volume Change (km )
-3.2 ± 2.7 km3/yr
Region 5
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y = 0.0664x - 1.7051
-20
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+0.8 ± 1.0 km3 /yr
Region 9
20
Water Equivalent Volume Change (km )
0
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2
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-40
40
10
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1
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-20
GRACE regionally-averaged water equivalent
thickness time-series, and least-squares derived
secular trend is shown in the left. The nearperiodic Seasonal variation is evident. The trend
of water equivalent thickness change is near-zero,
suggesting near-balance in water exchanges. The
region of GRACE data extraction is from 24.5 o N
o
o
o
to 35.5 N, and 65.5 E to 104.5 E.
Himalaya and
Tibet Tibet
Plateau Region
Himalaya
and
Region (red)
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y = -0.1245x + 3.92
60
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Water Equivalent Volume Change (km )
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Water Equivalent Volume Change (km )
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-60
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Water Equivalent Volume Change (km )
2
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-1.6 ± 1.7 km3/yr
Region 3
0
In this poster I have illustrated GRACE water equivalent mass changes, secular trends and variations, on the region
of the Himalaya Mountains and Tibet Plateau. Regionally averaged trends indicate both water equivalent volume
losses, on the central Himalayas, and increase on the northern Tibet Plateau. The next part of the investigation will
validate the secular trends and variations with available in-situ datasets. A recent paper by Ramillien et al. (2008)
using GRACE datasets on a global basis suggest that terrestrial water losses, as contributions to global sea-level
change, may become comparable in magnitude to those from the ice sheets.
0
-20
20
2
Prospective
-60
y = 0.1274x - 3.677
20
40
8
The GRACE datasets come from the Center for Space Research, University of Texas at Austin. These are the Release 4
Level 3 products, from August 2002 through December 2008, Land and Ocean monthly grids (Chambers, 2006b). The
grids were combined to give global land and ocean coverage, then adjusted by a Glacial Isostation Adjustment grid
provided by Paulson et al. (2007). Latitude-by-longitude regions were then extracted for each month, and the region
sample mean and standard deviation were computed. Least-squares trends were then derived. The region-average
time series and trends are shown at the center of the poster.
-40
+1.6 ± 0.9 km3/yr
Region 6
40
y = 0.25x - 8.3689
60
0
Method
0
-20
60
-60
0
(From D. Chambers, 2006a)
0
2
2
0
Water Equivalent Volume Change (km )
3
k l -- Love numbers
-60
-40
0
r -- Earth radius
t -- Time
f , l -- latitude and longitude
-40
0
0
]
1
0
0
a e -- Earth mean radius
r e -- Earth mean dinsity
r w -- Density of water
1
8
2
4 ln(2)
P lm : Normalized Legendre polynomials
D C lm, D S lm : Normalized time-varying Stokes spherical harmonic Geopotential coeficients
0
-20
-20
0
2
y = 0.2459x - 7.6631
20
y = 0.0488x - 1.3381
20
20
2
[
(lr / a e)
+3.1 ± 0.5 km3 /yr
Region 4
40
+0.6 ± 0.5 km3 /yr
Region 10
40
+3.1 ± 1.0 km3 /yr
Region 2
40
2
W l = exp
60
60
60
8
(1 + k l)
[Length unit: cm in water equivalent]
0
2
-60
1
l=0 m=0
W l P lm sin f [ D C lm (t) cosm l + D S lm (t) sinm l ]
y = 0.2804x - 9.8631
-40
0
SS
(2l + 1)
-60
-20
3
l
Water Equivalent Volume Change (km )
3 rw
120
-40
0
2
ae re
0
-20
20
2
The co-orbiting satellites of the Gravity Recovery and Climate Experiment (GRACE) do not measure variations
in gravity or mass directly (Chambers, 2006a). Rather, measurements in the variations of the inter-satellite range
(range rate and range acceleration) is measured, coupled with accurate GPS location relative to the International
Terrestrial Reference Frame 2005, to estimate values of the time change in spherical harmonic geopotential
coefficients, D C and D S, to degree and order 120 (Level-3 grids are complete to degree and order 40 however).
These are then used in the expansion below to estimate movement of water mass:
y = 0.0995x - 3.0734
20
+3.4 ± 1.4 km3 /yr
Region 1
+1.2 ± 0.3 km3/yr
Region 7
40
40
2
0
GRACE Surface Mass Change
60
Water Equivalent Volume Change (km )
3
Water Equivalent Volume Change (km )
60
0
The Himalayas and the Tibet Plateau form a region of about 3.4 million square kilometers. Home to numerous
large lakes and tarns (glacier lakes), and to more than 50,000 glaciers and high-elevation snowfields, this region
is the source of the Indus, Ganga, Brahmaputra, and Yamuna Rivers, the Indo-Gangetic River system. The
Himalayan Mountains and associated ranges form a boundary separating continental air masses associated
with the westerlies, and marine air masses associated with the summer South Asian monsoon. Adverse changes
in water storage / river discharge driven by effects of climate change will impact agriculture, hydroelectric
power facilities, commerce, and the lives of more than 1.3 billion people. Monthly water equivalent thickness,
i.e. hydrologic mass balance, from the Gravity Recovery and Climate Experiment (GRACE) Level-3 Release 4
de-striped global grids from the University of Texas Center for Space Research are being investigated to assist
in assessment of hydrologic changes. Processing adjusts the GRACE monthly grids for modeled atmosphere
water mass, solid Earth and ocean tides and pole tides, and geoid. The D C 20 geopotential coefficient which
is caused by water mass transport is not modeled at this time. In this study, the monthly grids were adjusted
for glacial isostatic adjustment (Paulson et al., 2007; ICE-5G/VM2), and regional-averages were computed
for the Himalaya Tibet Plateau and the Eastern India Bay of Bengal to derive time series. Over the period
of the GRACE observations, August 2002 through December 2006, annular periodicity of the mass balance
is evident with minima occurring in May and maxima occurring in September. Comparison of the regional
time series shows near synchronized annular periodicities with high positive correlation. Least-squares
regression after removal of an annual periodicity, suggests the Himalaya Tibet Plateau had an area-average
water thickness reduction of 0.031 ± 0.019 cm/month, equivalent to a water volume loss of 17.9 ± 11.0 km 3/yr.
On continental regions, GRACE hydrologic mass balance can be composed of signals from changes in
groundwater storage, permafrost, soil moisture, glacier mass balance and seasonal snowfield loads, and river
discharge. Comparisons with other related geophysical datasets will be needed for validation, assessment
of uncertainty, and separation of source components of the GRACE monthly trends and variations of hydrologic
Mass balance.
D h ( f , l , t) =
GRACE Region Secular Trends
and Variations
GRACE Sub-Region Secular Trends and Variations
from 8-2002 through 12-2006
Abstract
Sub-dividing the Himalaya-Tibet region, as
shown in the center of the poster, indicates
water equivalent volume loss occurring on the
central Himalaya Mountains, which are home to
glaciers with large negative mass balances, on
average.
Further experiments with the GRACE secular trends and comparisons to in-situ data and models
are being conducted.